I added the M__exit__ method to file to support "with open() as f" but the execution fails as following:

>>> with open("testfile") as f:
...   print("hello")
... 
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
    FIXME line of source goes here
AttributeError: AttributeError: "'file' has no attribute '__exit__'"

The code in this case is only checking for the exit attribute instead of also checking for the implemented interface.

I see this comment:

 // exit := py.ObjectLookupSpecial(mgr, "__exit__")

But I am not sure of how ObjectLookSpecial could be implemented.

An easier way to do this, but it feels "wrong", would be to add an exit method in the object dictionary.